Feeding fodder beet (Beta vulgaris L.) versus pasture reduces methane emissions and nitrogen excretion in sheep

Fodder beet (FB; Beta vulgaris L.) is increasingly used in ruminant production systems, particularly in New Zealand. Its high contents of readily fermentable carbohydrate and low crude protein may reduce enteric methane emissions and nitrogen excretion when included in ruminant diets, provided animal health and livestock performance are maintained. This study evaluated the effects of replacing pasture [a mixture of perennial ryegrass ( Lolium perenne L.) and white clover ( Trifolium repens L.)] with FB (1:1 on a dry matter basis, without rebalancing to equalise crude protein) on methane emissions and nitrogen partitioning in sheep. Thirty-two 12-month-old male sheep (mean liveweight 40 ± 1.2 kg) were allocated to either an FB-based or a pasture diet (n = 16 each) and fed at 1.6 times their metabolisable energy requirements. Methane emissions (n = 12 each) were measured in respiration chambers in two experiments. Diets for the FB group contained 75% FB bulbs and 25% pasture (dry matter basis) in Experiment 1, and 90% FB and 10% pasture in Experiment 2. The 75% FB diet had greater digestibility and metabolisable energy value than pasture (n = 6 each; P < 0.05). Methane yield (g/kg dry matter intake) did not differ between the 75% FB and pasture diets, but was 13–16% lower when expressed per unit of digestible dry or organic matter. When FB formed 90% of the diet, methane yield decreased by over 60% ( P < 0.05), but the abundance of rumen bacteria associated with acidosis increased. Feeding 75% FB reduced nitrogen intake, urinary nitrogen excretion, and microbial protein production, and altered rumen microbiota, with increased Sharpea and decreased Ruminococcus . While FB can reduce environmental emissions at the animal level, its inclusion should not exceed 75% of the diet dry matter, and protein supplementation is required to maintain rumen health and nutritional balance. Further research under grazing conditions is needed to confirm these findings and establish practical feeding guidelines. • Compared methane production and nitrogen excretion from fodder beet and pasture diets • 75% fodder beet lowered methane yield by 13% – 16% per digestible dry matter • Methane yield dropped by over 60% when fodder beet formed 90% of the diet • 75% fodder beet reduced N intake, urinary N excretion, and microbial protein • Fodder beet shifted rumen microbiota, increasing Sharpea and reducing Ruminococcus